Police in Germany thought they had an open and shut case of drunk-driving when the dazed and confused owner of a wrecked car appeared before them badly hung-over and wearing nothing but his underpants.

But in fact the 54-year-old man had been the victim of a bizarre car theft which saw him driven around, while passed out drunk in the trunk of his Ford, by a car thief who was himself inebriated and high on marijuana.

The intoxicated robber later dumped his passenger by the side of the road in a sleeping bag, before turning the car over several times and escaping unharmed.

Officers had found the demolished car hours before the owner awoke half-naked on a pavement, wondering how he had got there.

"People are always making up stories," said a police spokesman in the western city of Dortmund Monday. "So for the first three days we suspected him."

Then a 31-year-old man arrived at the police station and confessed he had stolen the car after finding the owner lying in the open trunk snoring loudly.

The man related to astonished officers how he had drunk between four and five litres of beer and smoked several joints -- at the same party as his victim -- before taking off in and crashing the car without suffering any injury.

Police said the thief decided to confess after his girlfriend succeeded in pricking his conscience.